Because of concerns about the release of refrigerant gases to the atmosphere and the prohibition of knowingly venting refrigerants, especially ozone depleting refrigerants, there is a need for efficient automatic purging of noncondensable gases with only de-minimis release of refrigerant. My application accomplishes this on operating refrigeration systems. The disclosure of this is incorporated by reference. In a refrigeration system, it is well understood that air and noncondensable gases (herein after air refers to both air and noncondensable gases) can produce high head pressures and cause the compressor to operate at higher than normal temperatures. Air will react with the refrigerant and oil at the head of the compressor and cause decomposition and the formation of acids (hydrofluoric and hydrocloric.) Air can be trapped in the upper space of the receiver or can circulate through the system, induced by the velocity of the refrigerant. In the evaporator or the condenser, air can interfere with the heat exchange process.
Air can be present in a system because of incomplete evacuation after-pressure testing with nitrogen, by leakage of air into the system that operates under vacuum and by seepage of air into the system when opened for the repair or replacement of a component. In most cases, the customary method to remove air is to manually purge at the location where the system was opened or to pump the system down, shut off the compressor and manually purge from the top of the condenser. This is wasteful as refrigerant is released.
When refrigerant is recovered from a system, usually air can also be recovered and with present recovery machines it is trapped in the recovery tank. The partial pressure of the air adds to the saturation pressure of the refrigerant. This increased pressure slows down the recovery process and has to be manually purged from the top of the recovery tank.
Refrigerant reclaim and recovery systems that have methods for removing air are shown in U.S. Pat. Nos. 5,005,369 and 5,063,749 of Manz and U.S. Pat. Nos. 5,195,333 and 5,291,743 of Van Steenburgh,Jr. Other U.S. Patents for refrigerant recovery are shown in U.S. Pat. Nos. 4,766,733 and 4,981,020 of Scuderi.
It is necessary that the liquid level in recovery tanks be kept at a safe level, generally 80% full so that dangerous hydrostatic pressure can not result if the liquid refrigerant becomes warmer. The usual method of preventing overfilling of a recovery tank is to employ a liquid level float switch or an electronic weighing device that electrically connects with the circuit of the recovery machine to stop the recovery process.